A terminal, such as of power lines for transmission of high-voltage and high-current electric power, may be connected to a socket, and plug pins of a plug may make a hot-line connection to socket contacts of the socket so as to supply power source to an electrical device connected to the plug. In this case, at the moment at which the plug pins come into proximity to or separate from the socket contacts, there will be accumulated high electric energy between the plug pins and the socket contacts being brought into close proximity to each other, causing an arc discharge to occur therebetween. Such an arc discharge may also occur by an induced electromotive force that is produced when the plug pins connected to an inductive load is pulled out of the socket contacts of the socket connected to the power lines.
The arc discharge may readily occur at the instant when the plug pins of the plug come into proximity to or separate from the socket contacts in the process of insertion or extraction thereof. When the insertion or extraction force on the plug is released at such a position at which the plug pins and the socket contacts are in close proximity to each other, arc discharges may continuously occur, causing the plug and the socket to be heated and thus leading a danger of occurrence of fire.
The DC distribution connection device disclosed in Patent Literature 1 is configured such that the confronting surfaces of a plug and a socket, which face each other in the direction of insertion and extraction of the plug, are provided with a set of magnets and magnetic plates attracted by the magnets, which face each other, respectively, so that the plug pins and the socket contacts are attracted to each other at the connection position of the plug and the socket where the plug pins and the socket contacts make a hot-line connection to each other. According to the conventional DC distribution connection device, even when the insertion or extraction force is released at the intermediate insertion position of the plug pins at which the plug pins are in close proximity to the socket contacts, the plug is attracted toward the socket by the magnetic force by which the magnets attract the magnetic plates. This prevents the plug pins from stopping at such a position at which arc discharges continuously occur.